Conventional arrays of photodetectors typically multiplex detector amplitude information sequentially in time. The amplitude information is generally a function of the radiation flux incident upon individual detectors within a one or two-dimensional array of photodetectors. For example, an integrated circuit two-dimensional focal plane array of photodetectors may be responsive to incident radiation within the infra-red (IR) portion of the electromagnetic spectrum. Each photodetector within the array is typically defined as a unit cell of the array. Each unit cell may be further coupled to a unit cell of an associated readout circuit array wherein each readout unit cell may comprise an integrating transimpedance amplifier. Each transimpedance amplifier may have an output coupled to a multiplexer which sequentially outputs to a signal processor signals expressive the flux incident upon individual ones of the photodetector unit cells over a predetermined interval of time.
For focal plane and other applications the array of photodetectors is normally maintained at cryogenic temperatures within a Dewar. For example, the array may be maintained at approximately 77K by the operation of a liquid nitrogen cryrogenic system.
One problem associated with such conventional systems, due to the serial nature of the data stream, relates to the amount of time required to output all of the photodetector unit cells within the array. In order to provide for real-time detector operation it is often necessary to constrain the total number of unit cells to a number which may be read out and processed within an interval of time which is compatible with real-time operation. As a result, the imaging resolution of the array may be less than optimal for a given application.
Another problem associated with conventional imaging systems is that access to a particular unit cell or group of unit cells within the array is constrained by the sequential nature of the readout circuit. This may prove disadvantageous if it is desired to perform zoom, background subtraction, gamma suppression, offset/gain correction or similar operations. As a result, it may be necessary to provide high speed analog and digital signal processing circuitry with concomitant increases in system power consumption, electrical noise and package size.